http://elecraft.85.s1.nabble.com/Re-NOT-the-feedline-was-KPA-1500-faulting-on-6m-SWR-issues-tp7661502p7661543.html
Lets take another try at this. There still isn’t enough information in your emails to really determine what might be going on. From the amplifier’s viewpoint, *everything* from the antenna jack on the back of the amplifier is part of the antenna system. So far we know it consists of some section of RG213, another of LM400, a balun of some sort, and an antenna. There are undoubtedly some adapters and couplers in between, and perhaps a few other things. Knowing exactly what these are is critical in making any suggestions.
Every few months since we released the KPA500 we have seen emails from folks who are certain that the amplifier is causing a problem. We all build our stations for low power, then decide that adding an amplifier is needed, so we buy one. We then are faced with issues driving a lot more power into the antenna system. These are caused by deficiencies in that system, which was sized for much lower power, and almost always will contain at least one component that cannot handle the power. The last part of the KPA500 before power goes out is the directional coupler (note: it is after the low pass filters), the KPA1500 has its ATU after those components. With the KPA1500 ATU in bypass, the directional coupler becomes the last component. This is important because the directional coupler will see any problem in the antenna system, and report it. No amplifier component is in the way to modify things, we get a true picture of what follows the amplifier. So, when something glitches in the antenna system (usually an arc in a coupler, or an overheated toroid in a balun or matching unit), the directional coupler picks it up and moves to protect the amplifier.
With this in mind, place the KPA1500 ATU into bypass and perform the test. When you see the fault occur, you then need to look at the entire antenna system, starting at the antenna jack on the back of the KPA1500. All of the components are suspect, even a new part (balun, antenna, etc), which may have been affected by high power right after installation. Be sure to looks at the RG213, and at the coupler to the LM400. You have made reference to shack feed-through, what is that, and does it use components that might have issues?
As in past cases, find the problem in the overall antenna system, and the KPA1500 will be much happier, as will you.
> On Jun 1, 2020, at 2:25 PM, Peter Dougherty <
[hidden email]> wrote:
>
> Your point is valid, however the underlying fact in my situation is that the new antenna with the new 1:1 current balun (i.e. feedline choke) is presenting **identically** to my old antenna that didn't have a balun. Neither better nor worse.
>
> - pjd
>
> -----Original Message-----
> From:
[hidden email] <
[hidden email]> On Behalf Of Bob McGraw K4TAX
> Sent: Monday, June 1, 2020 4:48 PM
> To:
[hidden email]
> Subject: Re: [Elecraft] NOT the feedline
>
> Based on my experience, balun power ratings are for MATCHED conditions. It is rare that hams use a balun in a matched condition. Thus a 1:1 balun should see 50 ohms on the input and 50 ohms on the output, while a
> 4:1 balun should see 200 ohms on the output and 50 ohms on the input. In the case of a resonant folded dipole, a 4:1 balun is typically operating in a nearly matched condition. All others combinations are unknown and random.
>
> I run about 500 watts on all bands. My baluns are rated at 5KW! It takes 3 or 4 big hunkin' pieces of ferrite to attain this power level. My 6 meter balun is a 1/2 wavelength electrically of RG-213. No ferrite!
>
> Buy or build a balun of your choice. Using an IR temperature gun, measure the ambient temperature of the core. Run about 1/2 rated power carrier for 30 to 60 seconds. Measure the temperature again. If it is warm to hot, this is RF producing heat. And likely continuing will produce core failure. This is not a good balun for your application.
>
> One of my baluns work between the output of my KAT500 and the balanced feed line connected to the center of a 256 ft wire. That antenna works 160M - 6M with zero issues. Now, I do run a hybrid balun being a 4:1 Guanella balun as a transformer, and it is fed with a 1:1 balun for common mode rejection.
>
> Most single core, i.e. 2 or 3 cores stacked with 2 to 4 windings are not at all a proper balun design A Guanella balun will have 2 cores with 2 windings and then another 2 separate cores with another 2 windings. These are then wired to produce a 4:1 balun with good common mode rejection. Most "factory" 4:1 baluns are poorly designed and built junk.
>
> See
https://www.dj0ip.de/balun-stuff/ for further references.
>
> 73
>
> Bob, K4TAX
>
>
> On 6/1/2020 8:45 AM, Alan - G4GNX wrote:
>> I have a similar issue with ferrite 'balun' heating, although mostly
>> tested on 40 metres. I'm using an OSCFD (Windom) which has a main 4:1
>> balun at the feed point, but also has a sleeve 'balun' consisting of 8
>> ferrites wrapped in a plastic sleeve, about 3 feet from the feed
>> point. If I run the K3S at 100W, via the KPA500 in standby, then
>> through the KAT500 tuner, I see no problems.
>>
>> On increasing the power to 200W by using the KPA500 in Operate and
>> about 10W drive from the K3S, during a SSB 'over' the temperature of
>> the KPA500 rises and after a few minutes, the SWR readings on the
>> KPA500 and KAT500 start to rise. One of the Elecraft guys actually
>> very kindly went through my fault log and came to the conclusion that
>> the fault is with the antenna/feeder and I agree with him. What is
>> strange is that if I leave a solid carrier running at 200W, I can't
>> easily reproduce the issue and I wonder if its something being
>> affected by peak excursions with SSB?
>>
>> When things do start to go wrong, I can usually perform a manual tune
>> with the KAT500 and the fault will then not (mostly) be apparent.
>>
>> Anyway, I'm in the process of replacing the entire feeder with
>> Westflex 103 and much bigger ferrites. I will also replace the main
>> balun which is a 400W device for a 1KW device, as I think that running
>> the UK max of 400W may be pushing the spec of a 400W balun. Also, the
>> balun itself or connections to it may be faulty.
>>
>> The point now is that I have discovered some damage to the outer
>> covering of the sleeve 'balun' which may be the result of ferrites
>> overheating or may be the cause of movement of the ferrites thus
>> causing instability. Either way, heftier devices seem to be the order
>> of the day.
>>
>> Although the KPA500 temperature rise is somewhat expected, I feel it's
>> a bit higher over a short period than I would like and may be due to
>> reflected power.
>>
>> 73,
>>
>> Alan. G4GNX
>>
>>
>> ------ Original Message ------
>> From: "David Olean" <
[hidden email]>
>> To: "Peter Dougherty" <
[hidden email]>
>> Cc:
[hidden email]
>> Sent: 01/06/2020 13:25:18
>> Subject: Re: [Elecraft] NOT the feedline (was KPA-1500 faulting on 6m;
>> SWR issues)
>>
>>> Hello Peter
>>>
>>> I suspect RFI as well. I do not have a KPA1500, so my advice is not
>>> worth much, but the fact that the fault only occurs when a signal is
>>> being radiated sends me a red flag. I had a similar problem here
>>> with my SPE amplifier power output. I was measuring it on an LP-100A
>>> wattmeter. It turns out that 1.8 MHz energy from the SPE amp
>>> radiated from my vertical antenna and was getting into a new wire
>>> doublet antenna and coming back down the ladder line into the shack.
>>> The ladder line was about 7 inches from the power coupler for the
>>> LP-100A. RF caused the readings to go wacky and it looked like my
>>> amplifier was going postal! The problem was high rf fields next to
>>> the power meter coupler.
>>>
>>> Ferrite balun heating can be seen with a VSWR meter if you set the
>>> power at some intermediate level, key the amp up with a steady
>>> carrier, and watch for VSWR creeping up. Loose pins in coax can also
>>> be a problem. They can heat up and disconnect or start arcing. Those
>>> problems do not typically show VSWR creep. They happen all at once
>>> usually.
>>>
>>> The KPA1500 works fine into a dummy load. (No RFI) That is a big
>>> clue. Good luck and I hope you find the problem. Maybe an RF
>>> sniffer would detect the ingress point?
>>>
>>> 73
>>>
>>> Dave K1WHS
>>>
>>
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